In State v. Blackwell, 408 Md. 677, 971 A.2d 296 (2009), the Court of Appeals considered whether an officer's testimony regarding the administration and observations of a horizontal gaze nystagmus ("HGN") test to a defendant convicted of, among other things, driving a vehicle while under the influence of alcohol. At Blackwell's trial before the Circuit Court for St. Mary's County, the State's sole witness was Maryland State Trooper Jeffrey Linger ("Trooper Linger"), who stopped the vehicle Blackwell was operating on the morning we was arrested for the charged offenses. Id. at 681. Trooper Linger attested that, after stopping Blackwell, he administered two of three field sobriety tests on the defendant: the HGN and walk-and-turn tests. Id. at 681-82. During the State's direct examination of Trooper Linger, defense counsel objected to the officer's description of and conclusions reached from Blackwell's performance on the HGN test, which were overruled by the court. Id. at 682-84. At the conclusion of trial, the jury returned a verdict of guilty. Id. at 685. Blackwell appealed his convictions to this Court. Id. The Court reasoned that Trooper Linger's testimony regarding the HGB test was expert testimony "because it was based upon the officer's specialized knowledge and training." Id. at 685-86. Thus, the Court reversed Blackwell's convictions regarding the alcohol-related offenses, concluding that "the trial court erred in admitting Trooper Linger's testimony without having him qualified as an expert pursuant to Md. Rule 5-702." Id. at 686. The State filed a petition for writ of certiorari to the Court of Appeals, which was granted. Id. The Court of Appeals affirmed the judgment of this Court, concluding that the officer's "testimony about Blackwell's performance on the HGN test constituted expert testimony subject to the strictures of Md. Rule 5-702." Id. at 691. In reaching its conclusion, the Court noted that the officer reported, among other things, that Blackwell had "lack of smooth pursuit" and "distinct nystagmus at maximum deviation" in each eye. This testimony was not based upon the officer's general knowledge as a layperson but upon his specialized knowledge and training. To be sure, the HGN test is a scientific test, and a layperson would not necessarily know that "distinct nystagmus at maximum deviation" is an indicator of drunkenness; nor could a lay person take that measurement with any accuracy or reliability. Id. In addition, the Court rejected the State's assertion that Md. Rule 5-702 was "inapplicable because the officer did not expressly provide an opinion 'as to Blackwell's state of intoxication,'" noting that Md. Rule 5-702 provides that "expert testimony may be admitted . . . in the form of an opinion or otherwise . . . ." Id. at 693. The Court observed that when an expert describes firsthand observations in court, this basis testimony is generally still a form of expert testimony. Like ordinary percipient witnesses, such experts are reporting direct sense impressions. Unlike the nonexpert witness, however, the ability to make these observations in the first place typically requires expertise. A treating physician's description of symptoms, a fingerprint examiner's testimony about similarities or differences between two prints he has examined, or an engineer's description of what he observed when examining the prior art in a patent dispute are all examples of observational testimony that requires specialized knowledge. A lay observer of the same injuries, fingerprints, or inventions would lack either the vocabulary to describe what she saw with precision or the knowledge of which observation mattered. Id. As a consequence, the Court determined that "much like the doctor's description of symptoms, or the fingerprint examiner's testimony about the similarities or differences between two prints he had examined - both subjects of expert evidence - " the officer's observational testimony was based on specialized knowledge and experience and, therefore, expert testimony, because the average juror would not have known the correlation between alcohol consumption and HGN. Id. at 693-94.